The present invention relates to a process for the production of low ash fuel using calcined petroleum coke.
The main usage of the invention is to provide a process for the production of low ash, low phosphorus alternative fuel of moulded shape, hard, water resistant having chemical composition such that the product can be safely used in place of by-prpduct/bee-hive coke for industrial and/or metallurgical purposes.
Petroleum coke is produced during, refining of crude petroleum oil. After calcination, petroleum coke gives an excellent quality of carbonaceous material having very low ash, low volatile matter, low phosphorus and high fixed carbon content. The calcined petroleum coke has a very limited utility and at present to some extent is used in Electrode industry. It has no use in industrial/metallurgical purposes due to its physical and chemical properties which have made it unsuitable to withstand the burden in the furnace. Most of the oil refineries in the country have a very good stock of calcined petroleum coke. In recent years the demand for low ash metallurgical/industrial coke has increased manifold and the demand is rapidly increasing with the setting up of mini steel plants and foundries for production of high grade steel and casting materials of International Standard.
A process for producing low ash, tailor made fuel will augment the production of briquetted fuel of low ash, low phosphorus content, which can substitute the scarce low ash metallurgical/industrial coke in the low shaft furnaces, cupolas, etc, to produce high grade steel and casting materials Low ash briquetted fuel not only help to produce good quality product but also helps to increase the productivity which is bound to help the industry in a competitive market.
Metallurgical/industrial coke is produced by high temperature carbonisation of coal either in non-recovery type bee-hive ovens or byproduct recovery type coke ovens. For producing low ash, low phosphorus metallurgical/industrial coke, coal of low ash low phosphorus metallurgical/industrial coke, coal of low ash low phosphorus content has to be carbonised. But in India, the availability of low ash, low phosphorus content cooking coal is highly scarce which has compelled the iron and steel industry to import low ash low phosphorus metallurgical coke for production of high grade steel and casting materials. There are processes developed for producing briquette fuel using coal/coke breeze and processed coal tar as binder which can substitute the conventional coke used in metallurgical/industrial purposes. In Indian Patent No. 129108 a process has been described for production of weather resistant, hard, smokeless moulded fuels for industrial/metallurgical uses using coke breeze/char etc. All the processes mentioned above are for producing briquetted fuel which can substitute the conventional industrial/metallurgical coke. But like conventional coke the briquette fuel make from coke breeze is also high ash and moderately high phosphorus content. Such type of product is not suitable for producing high grade low phosphorous iron and steel. Present days, demand of the iron and steel industry is for low ash, low phosphorus metallurgical/industrial coke to produce high grade steel and foundry materials in an economic way to make the product competitive in the market. Prior to the present invention no process was developed and or processed tar for production fuel of low ash, low phosphorus content which can substitute the scarce low ash, low phosphorus content which can substitute the scarce low ash metallurgical/industrial coke. The present invention will eliminate the shortage of availability of low ash, low phosphorus metallurgical coke by briquetted fuel prepared by calcined petroleum coke which is plenty available in the country.
The main object of the present invention is to provide a process for the production of low ash fuel using calcined petroleum coke which obviates the drawbacks detailed above.
Another object of the present invention is to utilize the briquetted fuel for the production of special grade iron and steel as the content of ash and phosphorous in the product is much below than those present in by-product/bee-hive coke.
Still another object of the present invention is to produce a product of uniform size and shape which permits full utilization of the product and provides better air permeability through the bed.
A process for producing low ash, tailor made fuel using calcined petroleum coke augments the production of briquetted fuel of low ash, low phosphorus content, which can substitute the scarce low ash metallurgical/industrial coke in the low shaft furnaces, cupolas, etc, to produce high grade steel and casting materials.
Accordingly the present invention provides a process for the production of low ash fuel using calcined petroleum coke which comprises of crushing and screening of the calcined petroleum coke at 3 mm size, mixing the crushed and screened materials to achieve bulk density in the range of 760 to 800 Kg/m3, mixing 10-100% of the resultant calcined petroleum coke with 0 to 50% coke breeze, pre-soaking the mix so obtained with 5-10% water, mixing with binder followed by kneading in presence of live steam then briquetting and curing of the raw briquettes in a furnace in a controlled oxidising atmosphere, through a twin paddle mixer and a screw feeder and curing of the raw briquettes in a furnace where temperature is maintained at the desired level by generating hot fuel gas by combustion of coal in a controlled oxidizing atmosphere, to obtain the low ash fuel.
In one embodiment of the invention, Asphalt or processed low temperature tar is used as binder.
In a further embodiment of the invention, the binder is used in the range of 6 to 7%.
In another embodiment of the invention, the curing of briquettes is effected at a temperature in the range of 250 to 300xc2x0 C. for a period in the range of 2.5 to 5.5 hours.
Low ash fuel is produced according to the process of the invention by using calcined petroleum coke. Calcined petroleum coke is crushed and screened at 3 mm size, and then mixed to achieve bulk density in the range of 760 to 800 Kg/m3. Of the resultant calcined petroleum coke, 10-100% is mixed with with 0 to 50% coke breeze, the mix so obtained being pre-soaked with 5-10% water. The presoaked mix is then mixed with a binder followed by kneading in presence of live steam. Briquetting and curing of the raw briquettes in a furnace in a controlled oxidising atmosphere, through a twin paddle mixer and a screw feeder. Curing of the raw briquettes is done in a furnace where temperature is maintained at the desired level by generating hot fuel gas by combustion of coal in a controlled oxidizing atmosphere, to obtain the low ash fuel.
The product, comprising of low phosphorus alternate fuel of moulded shape, hard, water resistant, can be safely used in place of by-product/bee-hive coke for industrial and/or metallurgical purposes,
The product can be suitably and sized as per requirements of the Ferro-chrome, Ferro-Silicon, Ferro-manganese and allied industries. Binders like Asphalt of 80/100 grade, and processed low temperature tar are used which are readily available in the market and thus minimizes the cost towards the preparation of binder.
The process does not require any carbonization step to make the product smokeless, hard and water resistant which makes the process comparatively less energy incentive.
(a) The calcined petroleum coke obtained from oil refinery is screened at 3 mm. The plus 3 mm of calcined petroleum coke obtained after screening is crushed to below 3 mm and then mixed with minus 3 mm size fraction previously obtained by screening to achieve the bulk range of 760-800 kg/m3.
(b) The use of calcined petroleum coke at the range of 10-50% by weight, mixed with coke breeze (xc3x973 mm) gives higher strength in terms of point crushing strength and micum indices. The ash content of the product is also increased to the extent which will be helpful to maintain the slag viscosity in the furnace hearth.
(c) The calcined petroleum coke with or without coke breeze is then pre-soaked with 5-10% water by weight of dry solids. Then it is mixed with Asphalt of 80/100 grade used as binder. The proportion of solids; binder is maintained at 93:7 by weight of dry solids. The binder may be asphalt of 80/100 grade having softening point of 45-52xc2x0 C. or a cut fraction above 300xc2x0 C. having S.P. 45-52xc2x0 C. of coal tar obtained from low temperature/medium temperature carbonization of coal.
(d) The mixture is then thoroughly mixed and kneaded in the kneader unit in presence of live steam at a gauge pressure of 6.0 kg/cm2-8.0 kg/cm2 where the temperature of the mixture goes upto 70-90xc2x0 C.
(e) The hot mixture from the kneader is then fed to a twin paddle mixer to cool down the temperature of mixture at 50-60xc2x0 C.
(f) The mixture from the mixer as stated in (e) is then fed to twin roll briquetting press through a screw feeder/pan feeder. The mixture is briquetted by twin roll press at a pressure of 200-300 kg/cm2. The green briquettes obtained from the rolls are of shape and of weight between 25 gm to 380 gm depending on the dimension of the briquettes.
(g) The green briquettes are cured in the furnace in batches. The heating of the furnace and the control of the temperature at desired level is done by generating hot flue gas by combustion of coal in a controlled oxidizing atmosphere. The temperature of curing bed is raised by introducing hot flue gas to the briquettes placed in layers in a controlled condition. The final temperature of curing bed is raised to 250-300xc2x0 C. and the temperature is maintained in that range for about 2.5-5.5 hours depending on dimension of the briquettes.
(h) The cured briquettes are then taken out of the furnace and cooled in the atmosphere.
The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of the present invention.